BAGHDAD, Iraq (CNN) --A U.S. soldier was killed Wednesday in an attack on a convoy in Baghdad, bringing the number of American battle deaths in the Iraqi conflict to 148 surpassing the 147 killed in the 1991 Persian Gulf War.

Thirty-three of those deaths have come in attacks since President Bush declared an end to major combat operations in Iraq on May 1.

The convoy from the U.S. Army's 3rd Corps Support Command came under small-arms and rocket-propelled grenade fire Wednesday morning near the Abu Ghreib prison in western Baghdad. Three soldiers also were wounded.

Meanwhile, in an unsuccessful attack on U.S. forces Wednesday, Pentagon officials said a U.S. military C-130 transport plane was the target of surface-to-air missile fire when it was flying into Baghdad International Airport.

The missile fire did not hit the aircraft, which was able to land safely, the officials said. Officials said there had been intermittent incidents with missile fire in the past. It was unclear if Wednesday's missile attack would delay planned reopening of the airport to commercial traffic.

Gen. John Abizaid, the chief of U.S. Central Command, said U.S. forces are facing "a classical guerrilla-type campaign."

The resistance appears to be organized "at the regional level" and composed of mid-level members of Saddam's Baath party, Iraq's intelligence services and remnants of the Special Republican Guard, he said.

"It's low-intensity conflict in our doctrinal terms, but it's war however you describe it," Abizaid said. He said U.S. troops are doing "a magnificent job" combating that resistance.

U.S. military leaders -- including Defense Secretary Donald Rumsfeld and Abizaid's predecessor at Central Command, Gen. Tommy Franks -- have until now resisted characterization of the opposition American troops face in Iraq as guerrilla warfare.

Abizaid said there is no sign of central command-and-control among Iraqi resistance groups, but a regional command structure appeared to be developing.

"It is getting more organized, and it is learning," he said. "It is adapting. It is adapting to our tactics, techniques and procedures and we've got to adapt to their tactics, techniques and procedures."

U.S. troops also face attacks from terrorist organizations such as Ansar al-Islam, a radical Islamic group that operated from Kurdish-ruled northern Iraq before U.S. warplanes bombed their camps during the invasion, Abizaid said. There also are fighters that are either members of the al Qaeda terrorist network or their "look-alikes," Abizaid said.

But he said the remnants of Iraq's ruling party are the "primary threat" to American and allied forces.

Tenet testifies to Senate

CIA Director George Tenet testified Wednesday at a closed hearing of the Senate Intelligence Committee, where he was expected to face questions about his agency's handling of President Bush's State of the Union speech.

Tenet said July 11 he should not have allowed the January speech to retain a reference to a now-discredited report that Iraq had tried to buy uranium in Africa.

Many Democrats have said the administration exaggerated the threat posed by Saddam Hussein and that it lacks a coherent Iraqi policy.

U.S. Sen. Edward Kennedy, D-Massachusetts, said Tuesday that the United States went to war against Iraq "under false pretenses."

The Bush administration has "undermined America's prestige and credibility in the world," Kennedy said in a speech delivered at the Johns Hopkins University School of Advanced International Studies in Washington.

U.S. Sen. Chuck Hagel, R-Nebraska, said the administration had an interest in resolving the issue.

"Listen, it wasn't just the CIA involved here," Hagel said. "We had the vice president and his office involved, [Defense Secretary Donald] Rumsfeld, [National Security Adviser] Condi Rice, [Secretary of State Colin] Powell's people. This wasn't just a one-man show."

Hagel voted to give Bush the authority to go to war with Iraq, but he said last week the Bush administration's case for war was looking "weaker and weaker." On Monday, he told CNN, "There's a cloud hanging over this administration." (Full story)

Other attacks in Baghdad

In another attack Wednesday, a U.S. soldier from the 1st Armored Division was wounded in an explosion outside a bank in Baghdad's Mansour district, a military spokeswoman said.

In addition, a U.S. Marine died Tuesday after falling from his guard post on top of a building in Baghdad, according to U.S. Central Command.

On a highway near Baghdad International Airport, an apparent mine explosion wounded two U.S. soldiers.

According to the Pentagon, 222 U.S. troops have been killed in Iraq, including 148 in hostile fire, since the conflict began in March. In the Gulf War, there were 147 battle deaths and 145 deaths in nonhostile incidents.

Other developments

• The U.S. military is investigating the killing of Hadithah Mayor Muhammed al-Jighaifi and one of his sons. Hadithah is about 120 miles (192 kilometers) northwest of Baghdad.

• The Pentagon is considering one-year tours of duty for Army units in Iraq as part of its rotation plan to maintain the current troop level in the country at about 148,000, U.S. military officials said. If approved, it would be the longest U.S. combat deployment since the Vietnam War. However, officials said that no decision has been made. If the one-year rotation policy is approved, the Pentagon then is likely to fashion a new "leave" policy that will allow troops an extended vacation at the midpoint of their tours of duty.

• Gen. John Abizaid, the chief of the U.S. Central Command, said Wednesday that plans are in progress to replace the remainder of the U.S. Army's 3rd Infantry Division "most likely" during September. Abizaid said the units that replace them could spend as long as a year in Iraq. On Tuesday, officials disputed reports that the troops would be in Iraq indefinitely. The division's 3rd Brigade already is returning to Fort Benning, Georgia, via Kuwait. At its peak, the 3rd Division had about 16,500 soldiers in Iraq, according to Army officials.